This function returns a linked list of all the HID devices attached to the system which match vendor_id and product_id. If vendor_id is set to 0 then any vendor matches. If product_id is set to 0 then any product matches. If vendor_id and product_id are both set to 0, then all HID devices will be returned.

Parameters:

vendor_id

The Vendor ID (VID) of the types of device to open.

product_id

The Product ID (PID) of the types of device to open.

Returns:

This function returns a pointer to a linked list of type struct hid_device, containing information about the HID devices attached to the system, or NULL in the case of failure. Free this linked list by calling hid_free_enumeration().

Set the first byte of data[] to the Report ID of the report to be read. Make sure to allow space for this extra byte in data[]. Upon return, the first byte will still contain the Report ID, and the report data will start in data[1].

This function initializes the HIDAPI library. Calling it is not strictly necessary, as it will be called automatically by hid_enumerate() and any of the hid_open_*() functions if it is needed. This function should be called at the beginning of execution however, if there is a chance of HIDAPI handles being opened by different threads simultaneously.

Feature reports are sent over the Control endpoint as a Set_Report transfer. The first byte of data[] must contain the Report ID. For devices which only support a single report, this must be set to 0x0. The remaining bytes contain the report data. Since the Report ID is mandatory, calls to hid_send_feature_report() will always contain one more byte than the report contains. For example, if a hid report is 16 bytes long, 17 bytes must be passed to hid_send_feature_report(): the Report ID (or 0x0, for devices which do not use numbered reports), followed by the report data (16 bytes). In this example, the length passed in would be 17.

In non-blocking mode calls to hid_read() will return immediately with a value of 0 if there is no data to be read. In blocking mode, hid_read() will wait (block) until there is data to read before returning.

The first byte of data[] must contain the Report ID. For devices which only support a single report, this must be set to 0x0. The remaining bytes contain the report data. Since the Report ID is mandatory, calls to hid_write() will always contain one more byte than the report contains. For example, if a hid report is 16 bytes long, 17 bytes must be passed to hid_write(), the Report ID (or 0x0, for devices with a single report), followed by the report data (16 bytes). In this example, the length passed in would be 17.

hid_write() will send the data on the first OUT endpoint, if one exists. If it does not, it will send the data through the Control Endpoint (Endpoint 0).